1. Field of the Invention
This invention relates to an ink jet recording apparatus which performs various controls by presumed head temperature, more particularly, to ink jet recording apparatus in which stabilization of ink ejection and detection of unejection are done by means of presumed head temperature, and recording method herefor.
2. Related Background Art
Recording apparatus like printers, copying machines and facsimile terminal equipment are constructed to record images consisting of dot-patterns onto recording materials like plastic sheet.
Recording apparatus can be classified into ink-jet, wire-dot, thermal, laser-beam printers etc., according to the recording method.
The ink-jet printer (ink-jet recording apparatus) is constructed to apply ink drops coming from an opening in the recording head onto the recording material.
Recently, a large number of recording apparatus are used, and high-speed recording, high resolution, high-quality image, low noise are required for these recording apparatus. The ink-jet recording apparatus can be a recording apparatus that satisfies these requirements. As this ink-jet recording apparatus ejects ink from the recording head, stabilization of ink ejection and ejected ink quantity that is required to fulfill the above requirements are greatly influenced by the ink temperature at the ink ejection opening. If the ink temperature is too low, the viscosity of the ink will increase abnormally and the ink will not come out by normal ejecting energy; if the temperature is too high, the ejected ink quantity will increase and the ink will overflow on the recording paper, and it will lead to deterioration of printing quality.
Therefore, in the hitherto ink-jet recording apparatus a method of controlling the ink temperature at the ejection opening within a desired range using a temperature sensor mounted on the recording head, or a method of controlling the ejection recovery. As the heater for said temperature control, heating element mounted on the recording head is used, and in ink-jet recording apparatus in which the recording is done by forming flying liquid drops using heat energy, i.e. in such apparatus that eject ink drops by means of growing bubbles by ink film boiling, the ejection heater itself may be sometimes used for said purpose. By using said ejection heater it must be supplied with electric current to such an extent that no bubbling occurs. In recording apparatus in which ink drops are ejected by growing bubbles in solid or liquid ink by means of heat energy the ejection characteristics changes greatly depending on the recording head temperature, therefore temperature control of the ink and of the recording head that influences the ink temperature substantially is particularly important.
But when attempted to execute temperature control accurately by means of a temperature sensor mounted on the recording head, following problems can occur.
First, problem of the measurement error of the temperature sensor. In representative temperature sensor types such as thermistors and thermocouples, resistivity and electromotive force fluctuate according to the temperature. When detecting these fluctuating values, electric noises can occur, and it is extremely difficult to suppress these noises completely.
Secondly, there is the problem of the costs. In order to detect said temperature in addition to the thyristers and thermoelements amplifiers and antistatic components are needed; particularly the antistatic components lead to considerable increase of costs.
Particularly, in case of the recording apparatus having a exchangeable recording head, the recording head being a wear parts, the user detaches the head frequently from the recording apparatus. The power output of the temperature sensor goes from exchangeable recording head through the contact on the carriage, and through the flexible wiring unchanged to the circuit on the print circuit board in the main body. Therefore the temperature measurement circuit can easily be influenced by electrostatic noises, and when operating the ejection heater or temperature regulating heater noises occur under the influence of driving pulses or temperature regulating current, and therefore without considerable antistatic measures it is not possible to measure temperature exactly.
As for the temperature detection by temperature sensor, in order to avoid the detection error, a method is applied that the averaged value of the detected head temperatures detected several times in the past is used as the present temperature. But by averaging the several detected temperatures the dynamic temperature change at the recording head will be averaged, and time delay will occur between the real temperature and the detected value (bad response), it is not possible to conduct exact feedback control.
For these reasons, a method in which the temperature fluctuation is calculated from the energy supplied to the recording head within a time unit is suggested. However, this method has the following problems.
First, in this method the temperature fluctuation is calculated by accumulation of the hysterisis of the energy supplied to the recording head. Therefore between the real head temperature and the calculated head temperature error can occur. In recording apparatus equipped with a exchangeable recording head there is the problem of recording head difference. The recording heads mounted on the recording apparatus have various ejection quantities, heat radiation characteristics due to manufacturing errors, and different heat transfer rates because of the difference of elements (adhesive layer etc.). It is difficult to consider these differences into the calculation of the head temperature. As a result, between the real head temperature and the calculated head temperature error occurs.
The applicants suggest, in order to solve these problems, in the Japanese Patent Laid-Open Application Nos. 5-31906 (corresponding to U.S. Ser. No. 07/921,832, filed on Jul. 30, 1992), 5-31918 (corresponding to U.S. Ser. No. 07/921,932, filed on Jul. 30, 1992) and 5-64890 (corresponding to U.S. Ser. No. 07/852,671, filed on Mar. 17, 1992), to correct the temperature calculation using the detected temperature of the temperature detecting element in the recording head and a temperature presuming means.
In the Japanese Patent Laid-Open Application No. 5-31906 a high measuring precision is achieved by correcting the values (tables etc.) used for the calculation using the difference between the temperature detected by temperature detecting means on the recording head in a thermally stable state and the presumed calculated temperature. In the Japanese Patent Laid-Open Application No. 5-31918 the correction of the temperature detecting means is conducted by means of ambient temperature detecting means contained in the recording apparatus which operate at times at which recording is not done, or at times at which the temperature does not change. In the Japanese Patent Laid-Open Application No. 5-64890 the ratio of the temperature detected by the temperature detecting means to the calculated temperature is used to correct calculated temperature. These examples show methods to correct differences between individual temperature detecting means or differences of thermal time constants or thermal efficiencies at the time of ink-ejection between individual recording heads which are problems of exchangeable recording heads.
The temperature calculation method is to presume the temperature behavior (rising temperature) by presetting the degree of temperature by which the temperature of the object after rising by the supplied energy within a time unit by elapsing of each time unit falls, and by calculating the sum of the degree of the temperature at present to which temperature has fallen.
In the above methods it is desirable that throughput of the temperature presumption will be improved, and temperature calculation errors will be reduced.
In the recording head of an ink-jet recording apparatus it can occur that, if the head is left unused for a long time, particularly in the ink channel near the ejection opening, ink is not ejected normally because of increased ink viscosity. And, when ink ejection occurs continuously in such cases as recording with relatively high printing duty is performed, during the ejection fine bubbles can grow in the ink in the ink channels, and the bubbles remaining in the channels can influence the ejection, and as a result normal ejection will not be possible. Besides the above mentioned bubbles that grow in accordance with the ejection, at the joints in the ink supply lines can bubbles come into the ink.
The above mentioned unejection can not only reduce the reliability of recording apparatus but also damage the recording head itself and lead to a reduction of durability, because, when printing with high duty is performed by the recording head that cannot eject ink normally, the temperature at the recording head will rise considerably higher than in the case that the recording head is in the normal state.
As one of measures against these ejection failure resulting from varies causes, in ink-jet recording apparatus, the surface of the ejection opening on the recording head may be covered with a cap during no ink ejection to prevent the increase of ink viscosity. As an other means, in this capping state, from ejection opening, ink is sucked and ink with increased viscosity is discharged. As still another means, there is ejection recovery such as idle ejection in which ink is ejected into a certain ink sucking body consisting of ink absorber etc. to discharge high viscosity ink.
The ejection recovery of the above-mentioned means against the ejection failure is conducted automatically when the power was switched on, or during the recording at certain intervals, or by depressing the recovery button by the user whenever necessary.
But in ink-jet recording apparatus which performs the ejection recovery at the power-on, if the user switches power on and off frequently, the frequency of the ejection recovery can unnecessarily increase and ink consumption and the quantity of ink sucked from the ejection opening can increase. On the other side, in such recording apparatus types in which the user operates the recovery button according to his own decision, the user cannot know if the recording head is in the normal state or not, unless the printing is performed actually. Therefore these types are not sufficiently reliable at this point.
In the Japanese Patent Laid-Open Application No. 4-255361 filed by the present applicants a technic to decide if the recording head in a nonejecting state or not, according to the temperature rise at the recording head caused by idle ejection and the temperature fall occurring at the recording head after the idle ejection (these measures will be hereinafter referred to as "ink failure detection").
When power is switched on or after elapsing of a certain period of time after the switching on, failure detection is executed, and if the state of the recording head is decided as "ink failure detection", the ejection recovery is performed. By these measures unnecessary ejection recovery can be avoided, and ink consumption and waste ink can be reduced.
However, in this method, it takes a certain time to detect the unejection, and it was necessary to consume a considerable amount of ink. In case the detection of the unejection is performed after the power is switched on, if the head comes to the state of unejection for some reason, and if the user does not notice it, the recording apparatus would continue the printing operation, and the apparatus would be damaged by excessive rise of the recording head temperature.
Particularly, for example, if an ink-jet recording apparatus in which the recording head is supplied from an ink cartridge with ink, and when the ink cartridge has become empty the user replace it by a new one, does not have function of detecting the emptiness of the ink cartridge, the recording head will not be supplied with ink, and it would become the state of unejection. Every time this situation occurs, the recording head will be in danger by excessive temperature rise.